The invention relates to an assembly formed by at least one blade and a blade-fixing platform, and also to a method of manufacturing such an assembly.
The field of application of the invention is that of turbomachines, and particularly but not exclusively, making stator assemblies for turbomachines.
In conventional manner, turbomachine stator blades are fixed to top and bottom casings via platforms to which the ends of the blades are connected.
A commonly-used technique for connecting a blade to a platform consists in inserting an end portion of the blade in a socket in the platform together with an adhesive. Such a connection using adhesive can be inadequate.
When blades are made of composite material comprising plies of fiber reinforcement draped on a blade core, it has been proposed that the connection with the platform can be improved by extending the reinforcing plies beyond the end of the blade that is connected to the platform and by integrating the ply extensions with the platform. The reinforcing ply extensions extend as far as the zones where the platform is fixed to a casing so that they are themselves locally clamped between the casing and the elements for fixing the platform thereto.
The invention seeks to further improve the structural connection between a blade and a platform.
This object is achieved by a method in which the blade is made by draping fiber reinforcement plies on a blade core, with at least a fraction of the plies extending beyond an end of the blade for connection to the platform so as to form ply extensions, and in which the ply extensions are folded down onto the platform to form flaps that provide a structural connection between the blade and the platform, in which method, according to the invention, a part is used that constitutes a platform web, having a shape that is close to the shape of the platform with an inside face and an outside face that are opposite each other, the ply extensions are folded down against the inside face and against the outside face of the web of the platform so as to form flaps for securing the blade to the platform, and fiber reinforcement plies are draped around the web of the platform and over the flaps so as to form a platform box holding the flaps captive.
The method of the invention is remarkable in that it makes it possible to achieve a particularly strong socketed structural connection between the blade and the platform because of the presence of flaps which overlie both sides of the web of the platform and which are themselves held captive by plies which are draped around the web of the platform.
Advantageously, a fraction of the ply extensions and the end of the blade are engaged in a passage formed through the web of the platform and having a section of shape that corresponds to the end profile of the blade, these ply extensions and the blade end being engaged in the passage from the inside face of the platform web, and the ply extensions that have passed through the platform web being folded down against the outside face thereof, while other ply extensions that have not been inserted in the passage are folded down against the inside face of the platform.
Also advantageously, the plies draped around the core of the blade and the plies draped around the web of the platform are impregnated with a resin, and heat treatment is performed simultaneously on all of the impregnated plies while they are held in shape. It is possible to perform draping using pre-impregnated plies or to drape plies that are dry and subsequently impregnated by injecting resin in a mold using a conventional resin transfer molding (RTM) technique. As a result, a structural bond is obtained by simultaneous polymerization of the resin impregnating the plies draped around the core of the blade and of the resin impregnating the plies draped around the web of the preform.
The invention also provides an assembly comprising at least one blade of composite material and an assembly platform for the blade, as can be obtained by the above method.